1. Field of the Invention
This invention relates to a mechanical stabilizing structure for particle beam sources, electron or ion (field emission) guns, especially as used in photolithography applications such as semiconductor mask fabrication.
2. Description of the Prior Art
Electron and ion guns are well known. Typically an electron gun includes an electron beam source (also called a cathode) which is held in fixed relation to a magnetic or electrostatic lens assembly for focussing the electron beam. The electrostatic lens assembly is a set of annular electrodes for focussing the electron beam. The source and its support structures are connected to a source-motion ring for small adjustments in electron beam position with respect to the fixed lens.
One prior art source support structure uses a set of three rods extending vertically between the source-motion ring and a source attachment disk from which the source itself is suspended. FIG. 1 shows such a prior art electron gun in an exploded view including gun-module mounting plate (base plate) 1, source-motion ring 2, three source support rods 3, lens assembly 4, lens 5, extractor cap 6, aperture clamp 7, wires 8, spring assembly 9, suppressor 10, suppressor ring clamp 11, high voltage collars 12, source attachment disk 13, high voltage cover connectors 14, filament connectors 15, spring assemblies 16, springs 17, screws 18, screw 19, washers 20, aperture 21, emitter 22, screws 23, screws 24, octupole 25, beam skirt 26, screws 27, 28, cap screws 29, 30, spring assembly connector 31, washers 32, 33, 34, and wire 35. The vertical rods 3 extend between the source-motion ring 2 and the source attachment disk. Alternative prior art source support structures include long rods or cantilevered supports. All such structures are undesirably vulnerable to external vibration, reducing the accuracy of the electron beam.